Microwave ovens are conventionally used for convenient and easy heating of food and drink. A container, made of heat-resistant plastic sheet, and having a hermetically sealed lid, is widely used for microwave heating of fresh food as well as processed food. Food and drink can be packaged in such a container, and can be easily heated and cooked without removal of from the container.
Known microwaveable containers, having hermetically sealed lids, and capable of withstanding temperatures of around 120° C., release expanded steam generated through a hole cut in the top or in the rim of the lid, or through a slit cut in a part of lid. Expanded steam may also be released through a concave groove in the fitting section of the body of the container when the lid is in place. Such a container is described in Japanese Patent No. 3009863.
Problems are encountered with these conventional microwaveable food containers, especially when they are used for full-fledged cooking. The lid may be forced off the container body by steam pressure, or liquid may splash out of the container through the concave groove in the fitting section, making a mess inside the microwave oven, reducing the amount of liquid in the container, and resulting in either inadequate or excessive cooking.
Containers of the prior art have a structure suitable for warming foods, but are generally unsuitable for cooking food when the container is filled with water or broth, which is generally a requirement for cooking fresh food. Small openings or the like may be provided in a part of the container, but such openings may cause another problem in that they permit the entry of dust or dirt into the container.
An object of this invention is to overcome the above problems, and to provide a food container for microwave oven cooking, made of plastic sheet, in which processed food can be preserved and conveyed in a sealed condition, in which steam pressure can be controlled, which prevents broth from boiling over during heating and cooking, and which achieves a quality of cooking equivalent to that achieved using conventional cooking utensils such as a pot, a pressure cooker, or a caldron or the like, heated by a gas flame or an electric heater. More particularly, the invention achieves the same cooking result as achieved in conventional cooking when the heat is repeatedly adjusted from a high to a medium or low flame, and the position of the pot lid is adjusted relative to the pot in order to prevent broth from boiling over when food and broth, or cold or hot water are heated by conduction from a gas burner, electric element or the like.